TACS'91 is the first International Conference on Theoretical Aspects of Computer Science held at Tohoku University, Japan, in September 1991. This volume contains 37 papers and an abstract for the talks presented at the conference. TACS'91 focused on theoretical foundations of programming, and theoretical aspects of the design, analysis and implementation of programming languages and systems. The following range of topics is covered: logic, proof, specification and semantics of programs and languages; theories and models of concurrent, parallel and distributed computation; constructive logic, category theory, and type theory in computer science; theory-based systems for specifying, synthesizing, transforming, testing, and verifying software.

The present volume contains the proceedings of Logic at Botik '89, a symposium on logical foundations of computer science organized by the Program Systems Institute of the USSR Academy of Sciences and held at Pereslavl-Zalessky, USSR, July 3-8, 1989. The scope of the symposium was very broad; the topics of interest were: complexity of formal systems, constructive mathematics in computer science, denotational and operational semantics of programs, descriptive complexity, dynamic and algorithmic logics and schematology, formal tools to describe concurrent computations, lambda calculus and related topics, foundations of logic programming, logical foundations of database theory, logics for knowledge representation, modal and temporal logics, type theory in programming, and verification of programs. Thus, the papers in this volume represent many interesting trends in logical foundations of Computer Science, ranging from purely theoretical research to practical applications of theory.